When the callee becomes available, it will return the appropriate final status response. The called party is temporarily unavailable, but the server has decided to queue the call rather than reject it.
This response MAY be used to initiate local ringback.Ī server MAY use this status code to indicate that the call is being forwarded to a different set of destinations. The UA receiving the INVITE is trying to alert the user. The 100 (Trying) response is different from other provisional responses, in that it is never forwarded upstream by a stateful proxy. This response, like all other provisional responses, stops retransmissions of an INVITE by a UAC. This response indicates that the request has been received by the next-hop server and that some unspecified action is being taken on behalf of this call (for example, a database is being consulted). Provisional (1xx) responses MAY contain message bodies, including session descriptions. They never cause the client to send an ACK. Note that 1xx responses are not transmitted reliably.
A server sends a 1xx response if it expects to take more than 200 ms to obtain a final response. Provisional responses, also known as informational responses, indicate that the server contacted is performing some further action and does not yet have a definitive response. Other HTTP/1.1 response codes SHOULD NOT be used. Not all HTTP/1.1 response codes are appropriate, and only those that are appropriate are given here. The SIP response codes are consistent with, and extend to, HTTP/1.1 response codes.